This invention relates to a mechanism for detecting completion of ice formation in an ice making machine. More particularly, this invention relates to a mechanism for detecting completion of ice formation in an ice making machine, in which a multiplicity of freezing fingers formed on the lower surface of a freezing base plate are dipped in the water supplied to a freezing chamber defined in a water tray to carry out a freezing operation and form inverted dome-shaped ice pieces gradually around the freezing fingers, wherein completion of formation of ice pieces around the freezing fingers is designed to be detected easily and securely.
Various types of freezing systems have been proposed for automatic ice making machines for making a number of ice pieces such as cubes continuously, and they are suitably employed depending on the applications. For example, the following systems are known:
(1) a so-called closed cell system ice making machine having a multiplicity of freezing cells opening downward defined by a multiplicity of partitions crossing one another, to which water is injected upward to the respective freezing cells, which are cooled by an evaporator connected to a freezing system, from a water tray disposed below the freezing cells to form ice cubes gradually therein; PA1 (2) a so-called open cell system ice making machine having such freezing cells opening downward, in which water is sprayed upward directly into the freezing cells using no water tray to form ice cubes therein; and PA1 (3) a flow-down system ice making machine having a perpendicular freezing plate, in which water is supplied to flow down on one surface of the freezing plate to form a semicylindrical ice block on the corresponding surface.
These three types of ice making machines all employ a forced circulation system and have a water tank for carrying therein a predetermined amount of water to be frozen, and the water in the tank is fed by a pump to the freezing cells or to the perpendicular freezing plate disposed in a freezing unit, while the unfrozen portion of the water is recovered into the tank to recirculate it to the freezing unit. Accordingly, incidental equipments such as a water tank and a pump for circulating the water to be frozen become necessary in such types of ice making machines. This causes not only complication of the structure of the machine but also production cost elevation and enlargement of the machine. Meanwhile, there has already been proposed a more simplified ice making machine, in which freezing fingers extending downward from the lower surface of a freezing base plate provided with an evaporator thereon are dipped in a predetermined level of water carried in a water tray to form ice pieces around the freezing fingers. This type of ice making machine requires no mechanism for circulating the water to be frozen between the water tray and the water tank during the freezing operation, so that the structure of the machine can be simplified, leading to production cost reduction and down-sizing of the machine, advantageously.
As described above, the last mentioned ice making machine, in which ice pieces are designed to be formed around the freezing fingers merely by dipping them in the water carried in the water tray, enjoys a great advantage that the structure of the machine can be simplified. This type of ice making machine employes a technique of counting the time required for forming ice pieces by a timer as a means for detecting completion of ice formation. In such technique of controlling the freezing operation by a timer, however, the freezing operation is designed to be carried out within a preset time period by the timer in spite of the fact that the time necessary for forming a desired size of ice pieces varies greatly depending actually on the ambient temperature (outer air temperature), so that it can happen that the ice making machine proceeds with an ice releasing operation before ice pieces are fully formed, or that the freezing operation is continued even after formation of the desired size of ice pieces, and the ice pieces are combined with the adjacent ones and deformed, disadvantageously. Accordingly, it can be pointed out that the maintenance and repair of the ice making machine become troublesome, since the preset time in the timer must be adjusted depending on the change in the ambient temperature.